Atomic spectroscopic methods

Matrix interferences can be observed in a number of different forms. Components in the extract may interfere with excitation of electrons. Absorbance of light by unexpected metals or organic compounds, generally or specifically, would also cause interference. Another source of interference is the complex-ation of the analyte with extract components such that the metal of interest is protected from the heat source. Other interferences such as changes in the viscosity of the extract are also possible, although they are less common. Whenever soil samples are analyzed by atomic spectroscopic methods, it is essential to make sure that no interfering species are present in the soils. If they are, then steps must be taken to correct for these interferences. 

Owing to their superior fluorescent yield, heavy elements ordinarily yield considerably more intense XRF bands than the light elements. This feature can be exploited to determine the concentration of inorganic species in a sample, or the concentration of a compound that contains a heavy element in some matrix. Many potential XRF applications have never been developed owing to the rise of atomic spectroscopic methods, particularly inductively coupled plasma atomic emission spectrometry [74]. Nevertheless, under the right set of circumstances, XRF analysis can be profitably employed. 

Atomic spectroscopy is an excellent method of analysis for trace or ultratrace levels of many elements in the periodic table. The major disadvantage of all atomic spectroscopic methods is that they provide no information on the oxidation state of the element or its speciation. This disadvantage can be redressed by the use of selective reagents coupled... 

To understand the analytical selectivity of atomic spectroscopic methods, a basic knowledge of the different sources of interferences which may be encountered is essential. Therefore, the concept and relative magnitude of each interference will be described next and compared for the three main atomic detection modes. The following discussion is a sort of basic platform to understand and assess potential sources of error in any atomic technique we might need in our laboratory. 

Parsons, M.L. and A.L. Forster. 1983. Trace element determination by atomic spectroscopic methods— state of the art. Appl. Spectros. 37 411 —418. 

Many metal analyses are carried out using atomic spectroscopic methods such as flame or graphite furnace atomic absorption or inductively coupled plasma atomic emission spectroscopy (ICP-AES). These methods commonly require the sample to be presented as a dilute aqueous solution, usually in acid. ICP-mass spectrometry requires similar preparation. Other samples may be analyzed in solid form. For x-ray fluorescence, the solid sample may require dilution with a solid buffer material to produce less variation between samples and standards, reducing matrix effects. A solid sample is also preferred for neutron activation analyses and may be obtained from dilute aqueous samples by precipitation methods. 

A. Csikkel-Szolnoki, S. A. Kiss, S. Veres, Elemental analysis of tea leaves by atomic spectroscopic methods, Magnes. Res., 7 (1994), 73-77. 

As well as the atomic spectroscopic methods of flame photometry and atomic absorption spectroscopy microwave emission spectroscopic detection (MED) is being used more and more. MED combines high sensitivity in the picogram range with high selectivity for elemental analysis. It is as suitable for inorganic and organic compounds... 

Schematic Representation of the Energies Generated by Atomic Spectroscopic Methods... 

Atomic spectroscopic methods are used for the qualitative and quantitative determination of more than 70 elements. Typically, these methods can detect parts-per-million to parts-per-billion amounts, and, in some cases, even smaller concentrations. Atomic spectroscopic methods are, in addition, rapid, convenient, and usually of high selectivity. They can be divided into two groups optical atomic spectrometry and atomic mass spectrometry. ... 

Column 2 of Table 28-4 shows detection limits for a number of common elements determined by flame atomic absorption and compares them with those obtained with other atomic spectroscopic methods. Under usual conditions, the relative error of flame absorption analysis is on the order of 1 % to 2%. With special precautions, this figure can be lowered to a few tenths of 1%. Note that flame AA detection limits are generally better than flame AE detection limits except for the easily excited alkali metals. 

Atomic fluorescence spectrometry (AFS) is the newest of the optical atomic spectroscopic methods. As in atomic absorption, an external source is used to excite the element of interest. Instead of measuring the attenuation of the source, however, the radiation emitted as a result of absorption is measured, often at right angles to avoid measuring the source radiation. 

Ion chromatography has become an indispensable tool for the analytical chemist in the area of anion analysis. In many cases this method has superseded conventional wet chemical methods such as titration, photometry, gravimetry, turbidimetry, and colorimetry, all of which are labor-intensive, time-consuming, and occasionally susceptible to interferences. Publications by Darimont [1] and Schwedt [2] have shown, that ion chromatographic methods yield results comparable to conventional analytical methods, thus dissolving the scepticism with which this analytical method was initially met. In the field of cation analysis, ion chromatography is attractive because of its simultaneous detection and sensitivity. It provides a welcome complement to atomic spectroscopic methods such as AAS and ICP. 

Ion chromatography provides an alternative to atom spectroscopic methods for the determination of heavy and transition metals. Its main advantage is the simultaneousness of the procedure and the possibility to distinguish between different oxidation states. For example, the determination of iron(III), copper, and zinc in a chromic acid bath (Fig, 8-41) may be performed free of interferences despite the high chro-mium(VI) load. Fig. 8-42 illustrates the determination of heavy and transition metals in a nickel/iron plating bath. Both oxidation states of iron can be clearly distinguished via ion chromatography. 

Chapter 11 details the relevant methods of analysis for both metals and organic compounds. For elemental (metal) analysis, particular attention is given to atomic spectroscopic methods, including atomic absorption and atomic emission spectroscopy. Details are also provided on X-ray fluorescence spectrometry for the direct analysis of metals in solids, ion chromatography for anions in solution, and anodic stripping voltammetry for metal ions in solution. For organic compounds,... 

The various areas of atomic spectroscopy will be discussed in more detail in the experimental and applications sections of this chapter. However, in order to better appreciate the ranges of applicability and limitation of the various atomic spectroscopic methods, it is in order to proceed next to a consideration of the features of atomic electronic structure which form the basis for atomic line spectra and to the processes which result in the production of atomic absorption or emission spectra. 

Except for the direct analysis of arsenic in body fluids by atomic spectroscopic methods or neutron activation analysis, and cold acid solubilization of solid samples (containing mainly inorganic arsenic) followed by hydride AAS (Haswell et al.. 1988), most methods for total arsenic determination require a complete decomposition of all arsenic compounds present. This can be achieved by a number of dry and wet decomposition procedures that are amply described in the literature (see also the Chapter on Sample Treatment of this book). Thus only examples of the most frequently and successfully applied approaches for subsequent arsenic determination are given below. 

Atomic spectroscopic methods have an enormous advantage in their speed. The final determination of a single element by atomic spectroscopy can be made in a minute or less. Most voltammetric determinations take five minutes or more for the potential scan alone. However the situation can be reversed for multi-element determinations. Polarographic or voltammetric methods often allow the simultaneous determination of several species in the same solution. With the atomic spectroscopic methods each element would require a change of lamp and its realignment. 

Epstein, M. S. "Comparison of Detection Limits In Atomic Spectroscopic Methods of Analysis" - Chapt. 6 in this volume. 

Comparison of Detection Limits in Atomic Spectroscopic Methods of Analysis... 

Of all atomic spectroscopic methods, ICP-MS is unrivalled concerning its detection power (Bencs et al. 2003). Its capability to process fast transient signals is crucial for the combination with sample preparation methods that generate impulse signals, like e.g. ablation techniques or most on-line preconcentration systems. 

Table 5 Mineral determination using methods different from atomic spectroscopic methods ...

Figure 1 Principles of laser-based atomic spectroscopic methods using resonant laser excitation (A) scheme of different detection methods (B) energy level diagram and transitions for excitation, ionization, and radiative deexcitation processes.

Atomic spectroscopy. Atomic spectroscopic methods includes atmoci absorption (AA), inductively coupled plasma atomic emission (ICP-AES), and inductively coupled plasma mass spectroscopy (ICP-MS). These methods are based on emission and absorption of electromagnetic radiation by atoms and provide information about levels of different elements in the sample (except some light elements such as H, C, N, O, etc.)... 

To understand the analytical selectivity of atomic spectroscopic methods, a basic knowledge of the different sources of interference which may be... 

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